dumpzone RPC

A Node RPC dumpzone that dumps the state of the Handshake Zone into a file could be useful for building DNS infrastructure on top of hsd.

By default, the file could be output in the zone file format.
The definition of a zone file is here, section 5 - https://tools.ietf.org/html/rfc1035
A more clear example - https://ns1.com/resources/dns-zones-explained

Arguments

• filename - name of file to write to
• json - output the file in json
• detailed - add additional handshake specific information like auction state

Detailed mode should only be able to work with JSON output, since the point of outputting a zone file is to interoperate directly with DNS servers